The present invention relates to a display arrangement with display to two directions comprising a first display displaying to a first direction and a second display displaying to an essentially opposite second direction. The invention also relates to a terminal device comprising such a display arrangement.
Liquid crystal displays (LCD, Liquid Crystal Display) are at present very common especially in small size devices. They are displays thin in construction, consisting of transparent electrodes, a medium containing liquid crystals and polarization filters. One of the most common constructions is the so called twisted nematic (TN, Twisted Nematic) LCD-display. In it the molecules of a layer of liquid arranged between glass plates are directed in a desired direction using control voltages, at which the optical properties of the display elements change and create the desired pattern in the display.
FIG. 1 presents a cross section of the most commonly used twisted nematic liquid crystal display 12. Liquid crystal display 12 consists of transparent electrodes 3, liquid crystal layer 5 containing liquid crystal molecules 15 and polarization filters 1 and 9. Closest to the viewer (topmost in the figure) there is polarization filter 1, which is located on top of glass plate 2 protecting liquid crystal layer 5. Under glass plate 2 electrodes 3 (figures seen in the display) have been arranged using a conductive, transparent layer (for example indiumtinoxide, ITO). The glass plates can also be replaced with plastics, if a lighter and more robust construction is desired. The disadvantages of plastics are the high price and so far difficulties in manufacturing. A so called orientation layer 4 has been integrated on the surface of electrode 3. Liquid crystal molecules 15 in liquid crystal layer 5 which touch it are oriented and thus orient the whole liquid crystal layer 5 (the layer between orientation layers 4 and 6 containing liquid crystal molecules 15) in the desired way. On the other side of liquid crystal layer 5 there is orientation layer 6, and as next transparent electrode 7 alike electrode 3. The next layer is protective glass layer 8, in the bottom surface of which polarization filter 9 has been arranged. On the other side of polarization filter 9 there is reflector 10 which in the figure is reflecting light upwards.
The electric field controlling the display is arranged by connecting an electric field between display elements, or electrodes 3, arranged in a desired form, and electrode 7 using voltage supply 13 and switch 11. The operation of a liquid crystal display is based upon the fact that when there is no electric field in the display, light passes through layers 1-9 and is reflected back by reflector 10. In this case the background of the display seems light. When controlling control voltage 13 is connected between electrodes 3 and 7, the electric field generated by it twists liquid crystal molecules 15 in medium 5 in such a way that the light polarized using polarization filters 1 and 9 cannot pass through the construction but is absorbed in the construction. In this case the background of electrode 3 seems black. Different shades of darkness can be obtained by adjusting the control voltage level. The crossing of electrodes 3 and 7 forms a pixel. A multicolor liquid crystal display is manufactured by adding a color filter in each pixel. All colors can be produced with pixels provided with red, green and blue filters. In practice the color filter is a single layer, placed for example between lower glass plate 8 and electrode 7 (or between upper glass plate 2 and electrode 3), in which case the desired color is obtained when light is reflected upwards (in FIG. 1). The display can further be provided with a background light placed under reflector 10, in which case light passes through the reflector upwards in the figure and illuminates the display. The background light can be realized as an electroluminescense layer (a so-called EL-background light), which is illuminated when a voltage is brought over it.
Other kinds of prior known liquid crystal displays are a display based on dynamic scattering and a display based upon induced rotation (guest-host).
Even if a liquid crystal display is flat and as such requires little space, space can be a problem in small size devices, such as mobile telephones, in which it is striven for devices with as small outer dimensions as possible and which are as light as possible. At present there are devices with several displays. An example of these is Nokia 9000 Communicator, with two displays opposite to each other, one display of the telephone section towards the outside of the device and a second display of computer/organizer section towards the inside of the device. The display of the telephone section is smaller and thus requires less surface area. Both displays however have the same thickness and they thus increase the thickness of the device when folded against each other. The situation has been illustrated in more detail in FIG. 2, in which telephone section display D1 is topmost with the viewing direction from top downwards in the figure, and in which computer/organizer section display D2 is lower with the viewing direction from bottom upwards in the figure. The structure of the displays has been simplified a little here. In telephone section display D1 there are top- and bottom polarizers 1xe2x80x2 and 9xe2x80x2, and glass plates 2xe2x80x2 and 8xe2x80x2, between which there is structure 14xe2x80x2 (presented in FIG. 1 with reference 14), which has been omitted here because of simplicity, and reflector 10xe2x80x2. In computer/organizer section display D2 there are respectively top- and bottom polarizers 1xe2x80x3 and 9xe2x80x3, and the glass plates 2xe2x80x3 and 8xe2x80x3, between which there is structure 14xe2x80x3 (presented in FIG. 1 with reference 14), which has been omitted here because of simplicity, and reflector 10xe2x80x3. Displays D1 and D2 have been fixed in printed circuit boards PCB1 and PCB2, which in the device have been fixed to each other. In the printed circuit board it has preferably been fixed display driver circuits Drxe2x80x2 and Drxe2x80x3, which control the display (realizing the functions 11 and 13 in FIG. 1 for each pixel). The solution presented in FIG. 2 is vertically rather thick in the figure and thus significantly increases the size of the device in the direction in question. In a more advanced version of Nokia 9000 Communicator-device, which will be released in the summer of 1997, the construction has been made smaller by using only one printed circuit board and by fixing displays D1 and D2 on both sides of the printed circuit board.
Now a two-sided display element has been invented, by using which a display to two opposite directions can be realized and the thickness of said display construction can be reduced compared with previous solutions. In the invention the one and same display component or display material element is utilized in the realization of a first display displaying in a first direction and of a second display displaying in a second opposite direction. In this way a part of said display component (display material element) is used for the realizing of a first display displaying in a first direction and a second part of said component is utilized in the realization of a second display displaying in a second opposite direction. The common Display Material Element is preferably such a part of the display the direction of which as to the direction of viewing has no importance. Other parts (layers) of the display, the direction of which as to the direction of viewing has importance, are arranged in such a way that they are in the first and second display in reversed order and turned into opposite directions if required. The displays are formed next to each other displaying information to opposite directions.
The invention is particularly suitable for use in connection with a liquid crystal display, when both a first display displaying to a first direction and a second display displaying to a second, opposite direction are realized using the same liquid crystal layer and the same electrode layers.
Also other kinds of flat displays can be used in the realizing of the invention, at least as far as their structure is similar to that of a liquid crystal display, or comprises (when the cross section of the display is examined) in the middle a layer of display medium and on both sides of it electrodes (longitudinal and transverse conductors). The display medium layer usually defines the type of a display. Said display medium layer is for example in the case of a plasma display a gas (a layer of gas between the electrodes) and in the case of an electroluminescense display a semiconductor/phosphorus compound (a compound between the electrodes, usually ZnS:Mn).
In addition to a common display component flat displays often have layers, the order of which in the direction viewing has importance. At least a part of such layers are arranged for the first display on the same level with the in order same layer for the second display on the opposite side of the common display component. In this way it is obtained an approximately equally thick construction, in which the surface of a part of the element forms a first display displaying to a first direction and a second part of the element forms a second display displaying to a second opposite direction. In the case of a liquid crystal display such parts, the order of which as to the direction of viewing has importance, are polarizers and a reflector, when the upper polarizer, counted in the direction of viewing, of the first display is mounted on the same level with the lower polarizer and reflector of the second display and vice versa.
Preferably, a display element according to the invention is not fixed to any printed circuit board, but the driver circuits of the display can be fixed directly on (one of) the glass plates of the display for example using the chip-on-glass technique. The omitting of the printed circuit board further makes the construction thinner. Driver circuits are used to control the display element area in such a way that in the area of the first display the figures desired in the first display are obtained and in the area of the second display the figures desired in the second display are obtained.
The invention is characterized in that it comprises a component common to a first and a second display, the component comprising a display material layer of a certain size, and a first part of said display material layer forms a part of said first display and a second part of said display material layer forms a part of said second display.